This invention relates to concrete-casting and more specifically to a mold element for casting concrete.
In recent years prefabricated mold elements are widely used in the construction industry. For instance, a mold element of the type used comprises a mold panel of sheet metal having a height of 2 to 3 meters and any desired length such as 1 to 4 meters. Horizontal stiffening members are welded at equal distances one above another at the surface of the mold panel facing away from the mold cavity such as, for instance, U-beams secured with one flange to the panel whereas the other flange is free. At right angles to these U-beams, i.e. vertically when the element is mounted in position for casting, a number of mold beams are fastened to the other flange of the U-beams with equal spaces, for instance 90 mm, the bending resistance of said mold beams being calculated so that the beams will resist the lateral forces resulting from the casting and vibration of the concrete mass. The top ends of the mold beams are linked together with a distance member, and the bottom ends are fastened to a sill or block of concrete or wood which, in turn, is fastened to the floor. A plurality of stay members, such as three or four ones, are distributed along the length of the mold beams and positioned to extend between the opposed mold element to prevent bulging of the mold walls under the lateral pressure of the fluid concrete mass.
A serious disadvantage of a mold element of this known type is the need of a large number of stay bolts with nuts, and the accompanying laborious mounting and dismounting work. Another disadvantage will be seen in the cumbrious complementary work required to fill up and smooth the holes and irregularities remaining in the finished concrete wall after dismantling the mold.
An approach to solve the above problems is represented by a mold element described in the inventor's Great Britain Pat. No. 1,381,346, according to which each mold beam has two and only two coupling points at each of which a stay bolt can be positioned to extend between the two opposed mold elements to form a mold cavity between them, wherein one coupling point of each beam is located at the upper end thereof at or adjacent the upper edge of the mold wall, and the other coupling point is located at a position between 1/4 and 1/3 of the height of the beam from the bottom end thereof.
Thus, the mold element described in the above-mentioned Great Britain Patent presupposes the use of an upper stay bolt to take up the outward pressure of the newly cast concrete mass above the lower stay bolt. In the course of pouring the concrete mass into the mold, the initial amounts of the poured mass will only exert a quite neglectible lateral pressure on the lower free ends of the mold beams via the mold walls, and when the mold has been completely filled and the lower ends of the mold beams are subjected to the maximum lateral force which could cause the lower end of the mold beam to be bent outwards, this bending outwards will be counteracted by the pressure exerted by the poured concrete mass on the mold beam between the points of action of the two stay bolts. In this manner a self-compensating system of forces is obtained which ensures a substantial stress-relief of the mold beam as compared with a beam clamped between the extreme ends.
The mold element according to the above-mentioned British Patent has subsequently been developed to the extent that the upper stay bolt has been given the shape of a flat bar steel member acting simultaneously as a distance member of a fixed length and having an opening at each end, said flat bar steel member being with one end pivotally mounted at a mold beam of an opposed mold element already erected and adapted to be swung across the mold cavity and secured with its other end by means of a lock bolt to an upstanding lug at the mold beam of the opposed mold element. It has been found, however, that the assembling operation is associated with serious difficulties. In the course of erecting a mold element in parallel relationship and at a fixed distance from a previously erected mold element, it is lifted by means of a building crane and lowered until it reaches the cast concrete blocks or other distance members secured to the floor to define the thickness of the wall to be cast. However, the mold element suspended in the wires of the building crane will tend to swing in the long lift wires so that it will be difficult to get the holes in the lug of the opposed mold beam and the distance member in register to allow insertion of the lock bolt. In the course of dismounting the concrete mold after completed casting operation, when the lock bolts are pulled or knocked out of their engagement, they are frequently lost.